Lead has been used in a variety of industrial applications for many thousands of years. In the last hundred years, the toxic effects of lead have become apparent. In an effort to reduce reliance on lead, there has recently been extensive research into materials that could be used to replace lead.
In this regard, much effort has been focussed on producing metal composites that mimic the properties of lead. Since the density of lead is the most obvious characteristic to mimic, most efforts have concentrated on finding composites that have the same or similar density as lead. However, other important properties of lead have been largely ignored and, as a result, no completely satisfactory lead replacement has yet been found.
In addition to being non-toxic and to having a similar density to lead, a successful composite should have reasonable softness coupled with structural rigidity. Ideally the composite is substantially homogeneous and relatively cheap to manufacture in large quantities.
U.S. Pat. No. 5,279,787 discloses high density projectiles formed by mixing a high density with a lower density metal. This patent does not disclose a composite made from tungsten and bronze.
U.S. Pat. No. 5,760,331 discloses projectiles comprising a metal having a higher density than lead and a metal having a lower density than lead. This patent does not disclose a composite comprising tungsten and bronze.
U.S. Pat. No. 5,894,644 discloses lead-free projectiles formed by liquid metal infiltration. In one embodiment, ferrotungsten is infiltrated by molten copper, tin or brass. Such composites do not have sufficient homogeneity to possess desirable processing characteristics and properties.
U.S. Pat. No. 5,950,064 discloses lead-free shot comprising a mixture of three metal components. This patent does not disclose a composite formed by mixing tungsten with bronze.
There still remains a need for a composite materials having a suitably high density, suitable processing characteristics and suitable properties for a variety of applications.